Today, on the Feast of Saints Peter and Paul, Pope Benedict gave the pallium to 34 archbishops from 20 countries. The use of the pallium goes back at least to the early fourth century. It symbolizes the unity of the Church, by visually representing each archbishop's participation in the authority Christ gave to St. Peter to shepherd His flock. Prior to the investing, the pallia are laid on St. Peter's tomb beneath the high altar of St. Peter's Basilica in Rome. The Catholic Encylopedia article includes the following:
"Worn by the pope, the pallium symbolizes the plenitudo pontificalis officii (i.e. the plenitude of pontifical office); worn by archbishops, it typifies their participation in the supreme pastoral power of the pope, who concedes it to them for their proper church provinces. An archbishop, therefore, who has not received the pallium may not exercise any of his functions as metropolitan, nor any metropolitan prerogatives whatever; he is even forbidden to perform any episcopal act until invested with the pallium. Similarly, after his resignation, he may not use the pallium; should he be transferred to anotherarchdiocese. He must again petition the Holy Father for the pallium. In the case of bishops, its use is purely ornamental. The new palliums are solemnly blessed after the Second Vespers on the feast of Sts. Peter and Paul, and are then kept in a special silver-gilt casket near the Confessio Petri until required."
Below is the video of today's Pallium Mass at St. Peter's Basilica in Rome.
Pallium Mass (Part 2)